The unusual age-distribution of the disease produced by RS virus, and the severe response to infection in children vaccinated with an inactivated RS-virus vaccine make it important to determine whether the structure, overall strategy of replication or the assembly and maturation of RS virus have unique aspects that may contribute to its pathogenesis. We have purified respiratory syncytial virus, resolved its proteins into 6-8 polypeptides and sequentially separated these from the virion, making possible the first comparison between the structural polypeptides of the virus and their organization, with that of other RNA enveloped virus. With the exception of the differences in the molecular weights of the virion polypeptides, RS virus resembles the other paramyxoviruses. The same virion polypeptides are produced by both human cells (HEP2) and monkey cells (BSC-1) infected with the Long strain of RS virus. RS virus infected HeLa cells trypsinized at 18 hours after infection and then replated in virus growth medium, resume virus production without any lag. Over the next 20-25 hours, they produce approximately 25 pfu/cell. By means of metabolic inhibitors, it has been determined that protein synthesis and glycosylation, but not RNA synthesis are required for a full yield of virus. It was determined that the glycoprotein pool was the limiting factor for virus production in this system. We have also established a persistent virus infection in HeLa cells. The virus produced by the persistently infected culture is a small plaque mutant of RS virus that is not temperature sensitive. For the coming year we propose to continue our studies of the virus polypeptides produced by established cell lines of human, monkey and bovine origin and to study the characteristics of the virus produced by the culture of persistently infected HeLa cells.